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GMS Zeitschrift für Hebammenwissenschaft

Deutsche Gesellschaft für Hebammenwissenschaft e.V. (DGHWi)

ISSN 2366-5076

Concentration of tin in breastmilk after the use of pewter nursing caps by breastfeeding women for the treatment of painful nipples

Research Article

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  • corresponding author Andrea Komlew - Catholic University of Applied Sciences, Munich, Germany
  • Christine Hupfer - Bavarian Health and Food Safety Authority, Erlangen, Germany
  • Bernd Reuschenbach - Catholic University of Applied Sciences, Munich, Germany

GMS Z Hebammenwiss 2020;7:Doc03

doi: 10.3205/zhwi000017, urn:nbn:de:0183-zhwi0000174

This is the English version of the article.
The German version can be found at:

Received: December 14, 2019
Accepted: April 16, 2020
Published: September 7, 2020

© 2020 Komlew et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution 4.0 License. See license information at


Background: The use of pewter nursing caps for the treatment of painful and/or damaged nipples is widespread in Germany. It is not known whether components of tin dissolve when the caps are worn, are absorbed by the (damaged) skin and are detectable in breastmilk the next time the child is nursed. The statutory limit for infants is 50mg tin per kilogramme of food.

Objective: In preparation for a study on the effectiveness of pewter nursing caps for the treatment of sore nipples during breastfeeding, this study aims to determine whether the tin concentration in breastmilk after the use of pewter nursing caps exceeds acceptable levels for newborns.

Subjects and methods: The tin content of breastmilk which accumulated inside the cap was measured in an in vitro test after one, three and four hours of use. Further, the tin content in the breastmilk of 24 breastfeeding women with different stages of nipple damage was tested in an in vivo test between April and December 2018. The degree of damage to the nipples was assessed by the recruiting midwife using the Nipple Trauma Score. Breastfeeding women with a score=0 were included, as even breastfeeding women with no visible damage can experience painful nipples, which is the indication for the use of pewter nursing caps. All breastmilk samples were tested for tin content using atomic absorption spectrometry in the laboratory of the State Office of Public Health and Food Safety.

Results: The highest tin content in the in vitro test was 3.92 mg/kg, well below the 50 mg/kg recommended for infants. In the in vivo test, regardless of the severity of nipple damage, none of the 47 breastmilk samples (1 dropout) showed a critical level of tin.

Conclusions: There is no indication that any tin constituents will dissolve out of the alloy during use and be present in breastmilk the next time the child is breastfed. The study is an essential basis for now pending comparative efficacy studies.

Keywords: damaged nipples, pewter nursing caps, breastfeeding, breastmilk, tin content


Up to 96 percent of all women experience damaged or painful nipples when they start to breastfeed and this is one of the most common reasons for stopping breastfeeding early [10], [17], [35]. In the first 14 days after birth, “damaged nipples” is the most frequently given reason for stopping breastfeeding, followed by “not enough milk”, “baby having problems feeding” and breastfeeding problems such as “blocked milk ducts/mastitis”. Women who breastfed their babies for less than four months, gave “breast problems” as the most frequent reason for stopping [10]. Effective treatment for damaged nipples can help prevent complications such as blocked milk ducts/mastitis [16] allowing the mother and child to enjoy the health benefits of breastfeeding [4], [31]. While improving the latch and breastfeeding technique is discussed as a way of preventing damaged nipples, and comprehensive counselling and instruction from the hospital staff is recommended [16], the available data concerning treatment of damaged nipples is inconclusive. This research paper was preceded by a systematic overview of evidence-based treatment measures for damaged nipples during breastfeeding. The overview included guidelines, systematic reviews, randomised controlled studies, clinical studies without randomisation, quasi-experiments and scientific articles. Articles published in German and English between 1980 and 2017 were considered. In the selection of the studies, they were classified based on the evidence hierarchy [23] in accordance with AHRQ (Agency for Healthcare Research and Quality) recommendations. As a result, the overview primarily included studies with randomisation or at least well-designed studies without randomisation, to be able to draw a scientific conclusion about the effectiveness of the treatment being investigated for healing damaged nipples. Non-experimental studies, in other words pure expert opinions, were also examined but were not incorporated into the systematic overview.

Lavergne [20] and Riordan [28] studied the effect of applying teabags and heat pads to damaged nipples. Other research studies concentrated on the application of expressed breastmilk [1], [8], [25], [32] and lanolin [1], [5], [6], [8], [15], [24], [25]. Moreover, the impact of breast shells [5], [6], [13], [32], hydrogel pads [5], olive oil [14], antibiotic ointments or oral antibiotherapy [21] and different types of nipple ointment [7], [9], [19] on wound healing and pain relief has also been examined. With the majority of therapies, no significant improvement was observed; only the use of lanolin proved to be effective in some of the studies [1], [8]. These results do not justify routine treatment of damaged nipples with lanolin, however. Available studies, are contradictory with some studies showing no significant effects from the use of lanolin [15], [25], [27]. To date, no single therapy has proven its superiority in clinical studies regarding relief of pain associated with breastfeeding [26]. In the S3-Guidelines for the Treatment of Inflammatory Breast Disease during the Lactation Period, the application of lanolin and expressed breastmilk is recommended based on many years of practical experience. To date, there is no scientific evidence to support this recommendation [16].

Another method used by practitioners to treat damaged nipples are pewter nursing caps. These are metal caps made from food-safe pewter that are placed on the damaged nipples of the breastfeeding mother and secured with a nursing bra. Several effects have been discussed regarding the mode of action of the pewter caps. In as early as 1962, for instance, Winter [33] reported on the principle of moist wound healing. The epithelialisation of the damaged area was completed twice as quickly when covered than when exposed to air. Dyson et al. [11] confirmed the principle of moist wound healing. In their study there was evidence of more granulation tissue formation in the covered wound that was kept moist, than in the wound healing under dry conditions. When pewter nursing caps are used, the damaged nipple is permanently bathed in breastmilk and thus the principle of moist wound healing takes effect.

Tin is a semi-precious metal with antiseptic properties. Tin ions, similar to other metal ions such as silver, copper and iron have a harmful effect on bacteria and fungi [12]. Inside the pewter cap, a microclimate develops which accelerates the epithelialisation of the tissue and at the same time reduces pathogenic germs. Due to the exclusion of air, aerobic pathogens cannot survive. This combination of effects appears to have a positive impact on healing damaged nipples and reducing the pain levels of the affected mothers. Marrazzu et al. [22] conducted a pilot study (n=40) to examine the effect of silver-impregnated caps on the perception of pain of the breastfeeding mothers. After 7 and 15 days, the women in the group being treated with silver-impregnated caps reported significantly lower levels of pain than the women whose nipples were being treated with expressed breastmilk. Another possible effect could be produced by the caps’ protective function, preventing clothing from coming into contact with the injured nipples and having a cooling effect [30].

Although the effect of silver-impregnated caps has already been the subject of scientific investigation, to date there have been no scientific studies on the effectiveness or safety of pewter caps that could legitimate their use. The Institute for Embryonal Toxicology in Berlin has assessed pewter caps as safe. However, the Institute has no data on whether components of tin dissolve when the caps are worn, are then absorbed by the (damaged) skin and are detectable in the breastmilk the next time the baby is nursed [30].


To obtain the data to answer this question, with the help of the Bavarian State Office of Public Health and Food Safety (Bayerische Landesamt für Gesundheit und Lebensmittelsicherheit, LGL) in Erlangen, samples of breastmilk were obtained from women who had used the pewter nursing caps and then tested for tin content. The objective of the study was to measure the tin content in breastmilk from mothers who had used the pewter caps for damaged nipples. In so doing, the study also allowed us to investigate the health safety of the pewter caps for the treatment of damaged nipples. Excessively high levels of tin contamination in breastmilk would be undesirable from a health perspective. The statutory limit for infants is 50 mg tin per kilogramme of food [18]. The long-term objective is to be able to offer breastfeeding women an effective and safe therapy for damaged nipples on the basis of a scientific research.

Material and methods

As the research question can only be answered using laboratory tests, the “Residues, Contaminants and Consumer Goods” unit at the LGL was informed about the research project. The staff in the department agreed to conduct the laboratory tests and specified the methodological procedure. In a first step, the material composition of the pewter caps was tested using X-ray fluorescence spectroscopy. The tin content of the breastmilk which had accumulated inside the cap was then measured in an in vitro test under laboratory conditions. The results were below the critical levels for infant nutrition. Thus, in a last step, the tin content in breastmilk obtained under real-life conditions was measured (in vivo study).

Checking the material composition of the pewter caps

In a first step, the material composition of the pewter caps was carefully checked. The pewter caps were obtained from a standard manufacturer who confirmed that they use food-safe tin to make the caps. For the study, ten pewter caps were manufactured and each cap was engraved with a digit (numbered from 1 to 10). This ensured that the results could be assigned to the relevant cap. Before using the caps for research purposes, they were sent to LGL and the precise composition of each individual cap was determined on 06.02.2018 using X-ray fluorescence spectroscopy. In one of the caps, both the inner and outer surface were examined. The tin content was >99%. In the other nine caps, the measurement was restricted to the inner surface of the cap which comes into contact with the skin. Irrespective of the localisation of the measurement, the tin content was also >99% in this case. This examination excluded the possibility of the caps containing any harmful components (such as antimony for instance).

In vitro test

To test for the transfer of tin to breastmilk, an in vitro test was carried out on breastmilk that had previously not come into contact with the pewter caps. This breastmilk was then placed in a pewter cap and incubated at 37 degrees Celsius (body temperature). The tin content in the milk was then measured after one, three and four hours. To determine the tin content in the samples, for each sample, nitric acid, hydrochloric acid and hydrogen peroxide solution were added to 2 g of breastmilk using a microwave-assisted closed-vessel system (Multiwave 3000, Anton Paar GmbH) and this was then transferred to a clear digestion solution where the presence of tin could be detected in the form of inorganic tin cations (see DIN EN 13805). The tin content of the solution was quantified using an atomic absorption spectrometer with graphite tube technology (High-Resolution Continuum Source Atomabsorptionsspektrometer ContrAA 700, Analytik Jena) via a calibration curve based on tin solutions with a known tin content.

The sample solution was also transferred to the device’s graphite tube with a pipette. Once the furnace programme was started, the sample was firstly dried and then pyrolysed by the heat of the graphite tube. Further heating resulted in the release of tin atoms, which collected in the beam path of light with a wavelength of 286 nm and absorbed the light of this wavelength, which is specific to tin. Based on the absorption strength, using a calibration solution and by deducting the blank value it was possible to calculate the tin content of the sample. The process described here is based on DIN EN 15764 for determination of tin by flame and graphite tube atomic absorption spectrometry.

All samples were digested and analysed in duplicate determination.

In vivo study

The main study that followed analysed the tin content of breastmilk from breastfeeding mothers using pewter nursing caps under real conditions. The target population comprised healthy mothers who had recently given birth and who reported that they had visible tissue damage and/or were experiencing nipple pain during the breastfeeding period and had been using pewter nursing caps. The degree of damage to the nipples was assessed by the recruiting midwife using the Nipple Trauma Score [2]. Breastfeeding women with a score =0 were included, as even breastfeeding women with no visible damage can experience painful nipples, which is the indication for the use of pewter nursing caps. The test subjects were informed about the objective of the study. Only once informed consent had been received were the participants recruited for the research project. The mothers who had recently given birth were asked to pump 10–15 ml of breastmilk on two separate occasions. The first sample was collected after the breastfeeding mother had worn the pewter nursing cap for at least four hours. The second sample was collected from the same woman when she had not worn the nursing cap for 24 hours. The aim was 50 cases of mothers who had recently given birth (see Figure 1 [Fig. 1]).

For the first sample, the nipple should not have been washed before the sample was collected (collection of sample 1). For data collection, the same conditions were required as is the norm in real-life practice. The time between feeds in a healthy newborn is three to four hours, which is why this timeframe was selected to test for tin content.

For the collection of the second sample, the participating women were asked to pump 10–15 ml of breastmilk having not used a pewter nursing cap for at least 24 hours beforehand (collection of sample 2). This sample served as a comparative sample to be able to determine what level of tin content is still detectable when the caps are not used.

Lastly, the breastmilk samples were sent to the laboratory of the State Office of Public Health and Food Safety (Erlangen site) where they were tested for tin content using atomic absorption spectrometry. The relevant endpoint was the tin content of the breastmilk samples after the breastfeeding mother has used a pewter nursing cap. What was important here was that the tin content in the breastmilk (50 mg/kg) did not exceed the acceptable level for newborns. Moreover, the correlation between the degree of damage to the nipples or the length of time the pewter nursing caps were used and tin content was also analysed.

Ethical aspects

This study was conducted in keeping with fundamental ethical principles according to national law and the Declaration of Helsinki [34]. The test subjects and their children are not harmed in any way through their participation in their study. The study participants received comprehensive written and verbal information about the objectives, methods and the context of the study, as well as the expected benefits. Every test subject received a written information sheet to inform them about the objectives and implementation of the study. Participants were only included in the study once informed consent had been received. Every participant provided a written declaration of consent. The participants were informed that they are entitled to withdraw from the study at any time with no obligation to provide a reason for doing so. The results were made available to the study participants on request.


Results of in vitro test

The in vitro test showed a very low level of tin absorption in the breastmilk. The proportion increased with the amount of time the mother wore the pewter nursing caps (see Table 1 [Tab. 1]). The highest value of 3.92 mg/kg was recorded after the caps were worn for four hours. Although this milk will be disposed of and not actually fed to an infant, this value is well below the maximum level of 50 mg/kg of tin in foodstuffs for infants set forth by the EU [18].

Results of in vivo study

The sample for the in vivo study comprised 24 breastfeeding women with different stages of nipple damage (see Table 2 [Tab. 2]).

Access to the research field was obtained through freelance midwives. Firstly, the midwives were briefed about the data collection process and the study objective. The project was then explained to the breastfeeding women and once they had provided informed consent they were recruited for the project. The participating midwives provided the new mothers with the required pewter nursing caps, breast pump and sample containers for the breastmilk. Each breastfeeding mother provided two breastmilk samples. One test subject was unable to pump the comparison sample as she had stopped breastfeeding by that time. In all 47 breastmilk samples, the tin content was below the detection limit. The finding holds irrespective of the length of time the participant used the pewter caps or the stage of nipple damage.

The results of this study indicate that, in terms of the tin content of breastmilk, the use of pewter nursing caps can be assessed as safe. The pretest shows that when the caps are filled with breastmilk, small quantities of tin, well below the maximum safe level may be absorbed into the milk. It may be that this low level accounts for the healing effect of the caps. The test subjects responded well to using the caps and there were no allergic reactions such as blistering, redness, pustules or itching. The breastfeeding mothers reported that the pewter nursing caps had a pleasant cooling effect on the damaged tissue. Moreover, the protection from the chafing of clothing was also assessed positively.


To date, there is a lack of unified standards for the treatment of damaged nipples during breastfeeding. In the S3-Guidelines for the Treatment of Inflammatory Breast Disease during the Lactation Period, the application of lanolin and expressed breastmilk is recommended [16]. However, these recommendations are based on professional expertise rather than scientific evidence. In practice, rapid healing of damaged/bleeding nipples is observed after the breastfeeding mother has used pewter nursing caps. Presumably, the effect of the pewter nursing caps is comparable with that of silver-impregnated caps [22]. Both the precious metal silver and the semi-precious metal pewter have antiseptic properties. In combination with the exclusion of air within the cap when it is placed on the nipple and the effect of a moist environment on wound healing, this accelerates the healing of damaged nipples thus also alleviating pain [22]. In Great Britain the use of silver-impregnated nursing caps is more widespread, while in Germany pewter nursing caps are being marketed. That said, there are very few sources of supply of high-quality pewter caps in Germany. The two products are very similar in price. Breastfeeding mothers are generally not aware that pewter and silver-impregnated nursing caps can be used.

While a study has already been conducted proving the positive effect of silver-impregnated nursing caps [22], there are no such findings for pewter caps. Moreover, there is an absence of knowledge regarding the safety of using either pewter or silver-impregnated nursing caps. There is one position statement from the Institute for Embryonal Toxicology assessing the pewter nursing caps as safe [29]. However, this recommendation may be undermined by the fact that it is not supported by a data basis. The project described in this document aims to close this research gap. The results of this study indicate that the tin limit for infants is not exceeded in the breastmilk after the mother has used a pewter nursing cap. The use of pewter nursing caps can, therefore, as already recommended by the Institute for Embryonal Toxicology be classified as safe.

Due to the ambiguous data situation regarding treatment of damaged nipples during breastfeeding, no single measure can be recommended as the method of choice. The literature overview conducted as part of this study does, however, indicate that moist wound healing (which occurs when pewter and silver-impregnated nursing caps are used) has positive effects in terms of pain relief in the case of damaged nipples. The caps were well received by the breastfeeding mothers and they described them as easy to use. Another advantage of using the caps is that the infant does not absorb any contaminants or ointment residues next time they are nursed, unlike when creams or hydrogel compresses are applied. The infant is therefore not perturbed by any foreign substances when they are placed on the breast because pewter caps are odourless.

Something to bear in mind here is that there can be manifold reasons for women to experience pain during breastfeeding. In the event that, despite therapeutic measures and healed nipples the woman still finds breastfeeding painful, the differential diagnosis of Raynaud syndrome must be considered and thrush too can result in pain during breastfeeding [29].

The results presented here apply to the commercially available pewter nursing caps used in this study, which have a high percentage of pure tin in the alloy. The possibility that practitioners may use caps which contain the metalloid antimony (up to 2 percent in the alloy) cannot be excluded [30]. The results of this study cannot be transferred to these caps. Antimony is a potentially toxic metalloid, which is used in industry as a catalyst in the manufacture of PET bottles, for example. At a dose of 0.5 mg/kg body weight, antimony causes vomiting, diarrhoea and cramps [3]. Due to the potentially toxic effect, the State Office of Public Health and Food Safety has stipulated that antimony should not be used in the manufacture of pewter caps intended for use in the context of breastfeeding infants. Mothers, midwives and breastfeeding and lactation consultants should ensure that they only purchase pewter nursing caps manufactured to a high standard using a highly concentrated tin alloy.

At n=24, the number of test subjects was relatively low. The 50 test subjects originally planned could not be achieved due to the difficult conditions in the research field. A larger number of cases would have been preferable to create a wider data basis for the results. A large proportion of the test subjects in this study had a Nipple Trauma Score of 0 (n=17) and no externally visible damage to the nipples. A larger sample would have resulted in greater variability of nipple damage and would have allowed us to better test for the transfer of tin components in the case of partial-thickness damage. The lower number of cases has a limiting impact on the transferability of the results.


There is no health risk of the use of pewter nursing caps for damaged nipples. Given that the results of this study substantiate the safety of pewter nursing caps, the next step is to carry out an efficacy study. The positive effects on wound healing indicated by experience, which have resulted in widespread use should be investigated in a randomised controlled study.


This study was conducted as part of the Master's degree programme in Applied Care Research at the at the Catholic University of Applied Sciences, Munich (Katholische Stiftungshochschule München).

Competing interests

The authors declare that they have no competing interests.


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